U.S. Pat. Nos. 5,592,085 and 6,879,155 disclose methods for measuring the elasticity and viscosity distribution of the interior of a measurement object and displaying the measurements as an image by applying pressure waves to the measurement object from the exterior and using magnetic resonance imaging (MRI) to measure the displacement induced by the pressure waves that reach the interior. U.S. Pat. Nos. 5,187,147 and 6,687,625 disclose methods for measuring the elasticity distribution of a measurement object and displaying the measurements as an image by applying pressure to the measurement object from the exterior and using ultrasonic echoes to measure the displacement induced by the pressure that reaches the interior.
When acoustical waves are produced by irradiating one side of a measurement object with pulse light and causing the measurement object to absorb the pulse light energy, the acoustical waves are reflected by the two opposing end surfaces of the measurement object and travel back and forth within the measurement object. Jpn. J. Appl. Phys., Vol., 42, pp. L556-L558 (2003) describes a technique for finding the viscosity-to-elasticity ratio of a measurement object by detecting the energy of the acoustical waves as a function of time in the other side. Opt. Exp., Vol. 3, pp. 199-211 (1998) describes a method for measuring the elasticity distribution of a measurement object and displaying the measurement as an image by applying pressure to the measurement object from the exterior and using optical coherence tomography (OCT) to measure the displacement induced by pressure that reaches the interior.
Another known method is to measure the elasticity and viscosity of a measurement object by Brillouin light scattering. J. Randall and J. M. Vaughan, Proc. R. Soc. Lond., B214, pp. 449-470 (1982) describes a technique for achieving the necessary resolution of 100 MHz or less for Brillouin scattering spectroscopy and removing noise caused by elastic scattering, by using a fragment of biological tissue as the object of measurement and using connected etalons as a high-resolution variable light filter to disperse the scattered light. K. Hattori, et al., Jpn. J. Appl. Phys., 33, pp. 3217-3219 (1994) describes a method which is measuring a polymer as the object and which optical heterodyne detection is used. T. Horiguchi, et al., J. Lightwave Technol., 13, pp. 1296-1302 (1995) describes a technique which is measuring an optical fiber as an object and in which the distribution of a Brillouin frequency shift is measured along the longitudinal direction of the optical fibers.